This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present disclosure. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present disclosure. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of prior art.
1. Field of the Invention
The present disclosure relates to the field of well completions. More specifically, the present invention relates to the isolation of formations in connection with wellbores that have been completed using gravel-packing. The application also relates to a zonal isolation apparatus that may be set within either a cased hole or an open-hole wellbore and which incorporates alternate flow channel technology.
2. Discussion of Technology
In the drilling of oil and gas wells, a wellbore is formed using a drill bit that is urged downwardly at a lower end of a drill string. After drilling to a predetermined depth, the drill string and bit are removed and the wellbore is lined with a string of casing. An annular area is thus formed between the string of casing and the formation. A cementing operation is typically conducted in order to fill or “squeeze” the annular area with cement. The combination of cement and casing strengthens the wellbore and facilitates the isolation of the formation behind the casing.
It is common to place several strings of casing having progressively smaller outer diameters into the wellbore. The process of drilling and then cementing progressively smaller strings of casing is repeated several times until the well has reached total depth. The final string of casing, referred to as a production casing, is cemented in place and perforated. In some instances, the final string of casing is a liner, that is, a string of casing that is not tied back to the surface.
As part of the completion process, a wellhead is installed at the surface. The wellhead controls the flow of production fluids to the surface, or the injection of fluids into the wellbore. Fluid gathering and processing equipment such as pipes, valves and separators are also provided. Production operations may then commence.
It is sometimes desirable to leave the bottom portion of a wellbore open. In open-hole completions, a production casing is not extended through the producing zones and perforated; rather, the producing zones are left uncased, or “open.” A production string or “tubing” is then positioned inside the wellbore extending down below the last string of casing and across a subsurface formation.
There are certain advantages to open-hole completions versus cased-hole completions. First, because open-hole completions have no perforation tunnels, formation fluids can converge on the wellbore radially 360 degrees. This has the benefit of eliminating the additional pressure drop associated with converging radial flow and then linear flow through particle-filled perforation tunnels. The reduced pressure drop associated with an open-hole completion virtually guarantees that it will be more productive than an unstimulated, cased hole in the same formation.
Second, open-hole techniques are oftentimes less expensive than cased hole completions. For example, the use of gravel packs eliminates the need for cementing, perforating, and post-perforation clean-up operations.
A common problem in open-hole completions is the immediate exposure of the wellbore to the surrounding formation. If the formation is unconsolidated or heavily sandy, the flow of production fluids into the wellbore may carry with it formation particles, e.g., sand and fines. Such particles can be erosive to production equipment downhole and to pipes, valves and separation equipment at the surface.
To control the invasion of sand and other particles, sand control devices may be employed. Sand control devices are usually installed downhole across formations to retain solid materials larger than a certain diameter while allowing fluids to be produced. A sand control device typically includes an elongated tubular body, known as a base pipe, having numerous slots or openings. The base pipe is then typically wrapped with a filtration medium such as a wire wrap or wire mesh.
To augment sand control devices, particularly in open-hole completions, it is common to install a gravel pack. Gravel packing a well involves placing gravel or other particulate matter around the sand control device after the sand control device is hung or otherwise placed in the wellbore. To install a gravel pack, a particulate material is delivered downhole by means of a carrier fluid. The carrier fluid with the gravel together forms a gravel slurry. The slurry dries in place, leaving a circumferential packing of gravel. The gravel not only aids in particle filtration but also helps maintain formation integrity.
In an open-hole gravel pack completion, the gravel is positioned between a sand screen that surrounds a perforated base pipe and a surrounding wall of the wellbore. During production, formation fluids flow from the subterranean formation, through the gravel, through the screen, and into the inner base pipe. The base pipe thus serves as a part of the production string.
A problem historically encountered with gravel-packing is that an inadvertent loss of carrier fluid from the slurry during the delivery process can result in premature sand or gravel bridges being formed at various locations along open-hole intervals. For example, in an interval having high permeability or in an interval that has been fractured, a poor distribution of gravel may occur due to a premature loss of carrier fluid from the gravel slurry into the formation. Premature sand bridging can block the flow of gravel slurry, causing voids to form along the completion interval. Similarly, a packer for zonal isolation in the annulus between screen and wellbore can also block the flow of gravel slurry, causing voids to form along the completion interval. Thus, a complete gravel-pack from bottom to top is not achieved, leaving the wellbore exposed to sand and fines infiltration.
The problems of sand bridging and of bypassing zonal isolation have been addressed through the use of Alternate Path Technology®. Alternate Path Technology® employs shunt tubes or flow channels that allow the gravel slurry to bypass selected areas, e.g., premature sand bridges or packers, along a wellbore. Such fluid bypass technology is described, for example, in U.S. Pat. No. 5,588,487 entitled “Tool for Blocking Axial Flow in Gravel-Packed Well Annulus,” and PCT Publication No. WO2008/060479 entitled “Wellbore Method and Apparatus for Completion, Production, and Injection,” each of which is incorporated herein by reference in its entirety. Additional references which discuss alternate flow channel technology include U.S. Pat. Nos. 8,011,437; 7,971,642; 7,938,184; 7,661,476; 5,113,935; 4,945,991; U.S. Pat. Publ. No. 2010/0032158; U.S. Pat. Publ. No. 2009/0294128; M. T. Hecker, et al., “Extending Openhole Gravel-Packing Capability: Initial Field Installation of Internal Shunt Alternate Path Technology,” SPE Annual Technical Conference and Exhibition, SPE Paper No. 135,102 (September 2010); and M. D. Barry, et al., “Open-hole Gravel Packing with Zonal Isolation,” SPE Paper No. 110,460 (November 2007).
The efficacy of a gravel pack in controlling the influx of sand and fines into a wellbore is well-known. However, it is also sometimes desirable with open-hole completions to isolate selected intervals along the open-hole portion of a wellbore in order to control the inflow of fluids. For example, in connection with the production of condensable hydrocarbons, water may sometimes invade an interval. This may be due to the presence of native water zones, coning (rise of near-well hydrocarbon-water contact), high permeability streaks, natural fractures, or fingering from injection wells. Depending on the mechanism or cause of the water production, the water may be produced at different locations and times during a well's lifetime. Similarly, a gas cap above an oil reservoir may expand and break through, causing gas production with oil. The gas breakthrough reduces gas cap drive and suppresses oil production.
In these and other instances, it is desirable to isolate an interval from the production of formation fluids into the wellbore. Annular zonal isolation may also be desired for production allocation, production/injection fluid profile control, selective stimulation, or gas control. However, the design and installation of open-hole packers is highly problematic due to under-reamed areas, areas of washout, higher pressure differentials, frequent pressure cycling, and irregular borehole sizes. In addition, the longevity of zonal isolation is a consideration as the water/gas coning potential often increases later in the life of a field due to pressure drawdown and depletion.
Therefore, a need exists for an improved sand control system that provides fluid bypass technology for the placement of gravel that bypasses a packer. A need further exists for a packer assembly that provides isolation of selected subsurface intervals along an open-hole wellbore. Further, a need exists for a wellbore apparatus that enables zonal isolation and flow control along a gravel pack within a wellbore.